EP1531978B1 - Pneumatic control method and device - Google Patents

Abstract

Disclosed are a pneumatic control method and device. A supply of a pneumatic operating means is controlled by means of at least one control device (41) between a source of said operating means and a receiving device for workpieces in the area of a supply line. A pressure which can be modified over time is generated by the control device (41) in the area of the receiving device. The control device is regulated such that a predefined pressure curve having a given maximum tolerance is generated at least around a pressure sensor (57).

Description

The invention relates to a method for the pneumatic control of a blow molding machine for the production of containers from injection-molded preforms, in which in the region of a supply line between a resource source for a pneumatic equipment and a receiving device for workpieces, a supply of the operating means is controlled by at least one adjusting device and wherein a time-varying pressure in the region of the receiving device is generated by the adjusting device.

The invention further relates to a device for blow-molding of containers with a heater for injection-molded preforms and a pneumatic control, one in the region of a supply line comprising between a resource source for a pneumatic equipment and a receiving device for workpieces arranged adjusting device which is driven to specify a time-varying pressure in the region of the receiving device.

Such methods and devices are used, for example, in connection with the production or further processing of blow-molded containers. One application in the manufacture of blow-molded containers is to specify a blow pressure curve. The default is typically done by a valve control, which initially switches on a lower blowing pressure and then a higher blowing pressure. Applications in further processing of blow-molded containers are in the context of plasma coatings in which sequential successive negative pressures with different pressure levels are supplied by valve actuators.

In a container molding by blowing pressure preforms of a thermoplastic material, such as preforms made of PET (polyethylene terephthalate), supplied to different processing stations within a blow molding machine. Typically, such a blow molding machine has a heating device and a blowing device, in the region of which the previously tempered preform is expanded by biaxial orientation to form a container. The expansion takes place with the aid of compressed air, which is introduced into the preform to be expanded. The procedural sequence in such an expansion of the preform is in the DE-OS 43 40 291 explained.

The basic structure of a blowing station for container molding is in the DE-OS 42 12 583 described. Possibilities for tempering the preforms are in the DE-OS 23 52 926 explained.

Within the blow molding apparatus, the preforms as well as the blown containers can be transported by means of different handling devices. In particular, the use of transport mandrels, onto which the preforms are plugged, has proven to be useful. The preforms can also be handled with other support devices. The use of tongs for handling preforms and the use of expansion mandrels which are insertable for mounting in a mouth region of the preform are also among the available constructions.

The already described handling of the preforms takes place firstly in the so-called two-stage process, in which the preforms are first produced in an injection molding process, then temporarily stored and later conditioned in terms of their temperature and inflated to a container. On the other hand, there is an application in the so-called one-step process, in which the preforms are suitably tempered and then inflated immediately after their injection molding production and sufficient solidification.

With regard to the blow molding stations used, different embodiments are known. In blow stations, which are arranged on rotating transport wheels, a book-like unfoldability of the mold carrier is frequently encountered. But it is also possible to use relatively movable or differently guided mold carrier. For stationary blowing stations, in particular are suitable for receiving a plurality of cavities for container molding, typically plates arranged parallel to one another are used as mold carriers.

From the DE-A-100 28 932 a control device for a handling device is known in which a movable piston in a cylinder is used. An actuation is carried out using a pressure regulator, which evaluates a sensory detected pressure.

From the GB-A-22 03 195 a control device for a pneumatically driven piston is known. The piston can be pressurized on two sides to perform a positioning and a piston position is detected by sensors.

In the GB-A-914691 An electropneumatic control system for extrusion blow molding machines is described. Using the control system, it is possible to control the blowing pressure in the area of the extrusion device.

From the US B1-6,264,457 For example, an input device is known, with which preforms are fed into a blow molding machine. The trained as a spur input device is actuated by a servo drive. An input device for the preforms is constructed using a fluid cylinder.

The known methods and devices are limited to perform a control of the actuators and to accept the resulting actual pressure curve. A concrete pressure course depends on a large number of currently existing process boundary conditions and changes with changing ones Process constraints. Investigations as to whether the resulting pressure profiles actually represent at least approximately optimal temporal pressure profiles with regard to a process optimization have not been carried out so far.

Object of the present invention is to improve a method of the aforementioned type such that an optimized process flow is supported at the same time simple device implementation.

This object is achieved in that the adjusting device is controlled such that a predeterminable time course of the pressure during the execution of a blowing process is generated at least in the environment of a pressure sensor with a predetermined maximum tolerance and that the time course of a process pressure of a blowing gas for expansion of the preform is set in the container.

Another object of the present invention is to construct a device of the aforementioned type such that both achieves a simple structural design and an advantageous process flow is supported.

This object is achieved in that the adjusting device is coupled to a control device which has a connection to at least one pressure sensor and that the control device has a history memory for a setpoint profile of the time pressure curve during the execution of a blowing process and is coupled to a flow control, the cyclically predefines a generation of the pressure curve according to the stored setpoint profile such that the time course of a process pressure of a blowing gas for expansion of the preform is defined in the container.

By controlling the pressure according to a time-varying setpoint profile, it is possible to provide an adapted to the respective current process state optimum pressure profile. The process control is thus not dependent on a more or less random setting depending on boundary conditions temporal pressure curve, but regulated and reproducible depending on a defined predetermined profile.

In addition to the process optimization to be achieved, a device-technical simplification can also be realized. According to the state of the art, several valves are typically used in order to connect different pressure levels one after the other in a time-dependent manner. Due to the regulation of the pressure curve according to the invention, it is generally sufficient to use a single adjusting device which adjusts the respective pressure level.

A fully automatic control is particularly supported by the fact that an electromechanically actuated valve is controlled as a control device.

To adapt to different application requirements, it is proposed that the setting device is controlled by a programmable controller.

A particularly preferred embodiment is that a proportional valve is actuated as an adjusting device.

In order to support both a holding of a predetermined pressure as well as a lowering or an increase in the pressure is provided that a three-way proportional valve is actuated as an adjusting device.

A typical application is that the pressure is controlled when performing a blowing process.

To support high production rates, it is proposed that a pressure supply be controlled for at least one blowing station positioned on a rotating blowing wheel.

In order to support a low-tolerance pressure realization at the intended application, it is proposed that the regulating device provide the regulated pressure with a small spatial distance to the receiving device.

A compact design with high control quality is also supported by the fact that the adjusting device is transported together with the receiving device by a rotating support wheel.

In blast engineering applications, in particular, it is provided that an overpressure is controlled.

Full applicability is supported by controlling a pressure with a pressure level up to 40 bar.

Improved control quality can be provided by controlling the pressure from a two-stage proportional valve.

A compact arrangement with simultaneously low-loss and very accurate control is achieved in that the adjusting device is provided with a at least partially closed by a valve body flow path.

A typical construction is that an interior of the actuator is connectable to the resource source via a pressure inlet.

It is also contemplated that the interior of the actuator is connectable via a vent port with an environment.

A connection of the intended receiving device for the workpieces takes place in that the interior of the adjusting device is connectable via a pressure outlet with the receiving device.

A scheme with low energy consumption is supported by the fact that the valve body is arranged positionable by an electrically controlled proportional solenoid against a force of a return spring.

Fig. 1

Eine perspektivische Darstellung einer Blasstation zur Herstellung von Behältern aus Vorformlingen,

Fig. 2

einen Längsschnitt durch eine Blasform, in der ein Vorformling gereckt und expandiert wird,

Fig. 3

eine Skizze zur veranschaulichung eines grundsätzlichen Aufbaus einer Vorrichtung zur Blasformung von Behältern,

Fig. 4

eine modifizierte Heizstrecke mit vergrößerter Heizkapazität,

Fig. 5

eine schematische Darstellung eines zweistufigen Proportionalregelventils,

Fig. 6

eine schematische Darstellung einer als Proportionalventil ausgeführten Stelleinrichtung mit Regeleinrichtung und

Fig. 7

beispielhafte Verläufe für zeitabhängige Druckprofile bei der Durchführung eines Blasvorganges.

In the drawings, embodiments of the invention are shown schematically. Show it:

Fig. 1

A perspective view of a blowing station for the production of containers from preforms,

Fig. 2

a longitudinal section through a blow mold, in which a preform is stretched and expanded,

Fig. 3

a sketch to illustrate a basic structure of a device for blow molding containers,

Fig. 4

a modified heating section with increased heating capacity,

Fig. 5

a schematic representation of a two-stage proportional control valve,

Fig. 6

a schematic representation of a running as a proportional valve actuator with control device and

Fig. 7

exemplary courses for time-dependent pressure profiles when performing a blowing process.

The use of the pneumatic control device will be to control the blast air supply in a blow molding apparatus. The basic structure of a device for forming preforms (1) in container (2) is shown in FIG. 1 and in FIG. 2.

The device for forming the container (2) consists essentially of a blowing station (3), which is provided with a blow mold (4) into which a preform (1) can be inserted. The preform (1) may be an injection-molded part of polyethylene terephthalate. To allow the preform (1) to be inserted into the blow mold (4) and to allow the finished container (2) to be removed, the blow mold (4) consists of mold halves (5, 6) and a bottom part (7), which is a lifting device (8) is positionable. The preform (1) can be held in the region of the blowing station (3) by a transport mandrel (9) which, together with the preform (1), passes through a plurality of treatment stations within the device. But it is also possible to use the preform (1), for example via pliers or other handling means directly into the blow mold (4).

To enable a compressed air supply line is below the transport mandrel (9) a connecting piston (10) arranged, which feeds the preform (1) compressed air and at the same time performs a seal relative to the transport mandrel (9). In a modified construction, it is basically also conceivable to use solid compressed air supply lines.

A stretching of the preform (1) by means of a stretch rod (11) which is positioned by a cylinder (12). In principle, however, it is also conceivable to perform a mechanical positioning of the stretch rod (11) via curve segments, which are acted upon by Abgriffrollen. The use of curve segments is particularly useful when a plurality of blowing stations (3) are arranged on a rotating blowing wheel. A use of cylinders (12) is expedient if stationarily arranged blowing stations (3) are provided.

In the embodiment shown in Fig. 1, the stretching system is designed such that a tandem arrangement of two cylinders (12) is provided. From a primary cylinder (13), the stretch rod (11) is first moved to the area of a bottom (14) of the preform (1) before the beginning of the actual stretching operation. During the actual stretching process, the primary cylinder (13) with extended stretching rod together with a carriage (15) carrying the primary cylinder (13) is positioned by a secondary cylinder (16) or via a cam control. In particular, it is envisaged to use the secondary cylinder (16) in such a cam-controlled manner that a current stretching position is predetermined by a guide roller (17) which slides along a curved path during the execution of the stretching operation. The guide roller (17) is pressed by the secondary cylinder (16) against the guideway. The carriage (15) slides along two guide elements (18).

After closing the mold halves (5, 6) arranged in the region of carriers (19, 20), the carriers (19, 20) are locked relative to one another by means of a locking device (20).

To adapt to different shapes of a mouth portion (21) of the preform (1), the use of separate threaded inserts (22) in the region of the blow mold (4) is provided according to FIG.

Fig. 2 shows in addition to the blown container (2) and dashed lines drawn the preform (1) and schematically a developing container bladder (23).

Fig. 3 shows the basic structure of a blow molding machine, which is provided with a heating section (24) and a rotating blowing wheel (25). Starting from a preform input (26), the preforms (1) are transported by transfer wheels (27, 28, 29) into the region of the heating path (24). Heater (30) and fan (31) are arranged along the heating path (24) in order to temper the preforms (1). After a sufficient temperature control of the preforms (1), they are transferred to the blowing wheel (25), in the region of which the blowing stations (3) are arranged. The finished blown containers (2) are fed by further transfer wheels to a delivery line (32).

In order to be able to transform a preform (1) into a container (2) in such a way that the container (2) has material properties which ensure a long useful life of foodstuffs filled inside the container (2), in particular drinks, special process steps must be taken the heating and orientation of the preforms (1) are maintained. In addition, you can advantageous effects can be achieved by compliance with special dimensioning rules.

As a thermoplastic material different plastics can be used. For example, PET, PEN or PP can be used.

The expansion of the preform (1) during the orientation process is carried out by compressed air supply. The compressed air supply is in a Vorblasphase in which gas, for example, compressed air, is supplied at a low pressure level and divided into a subsequent Hauptblasphase in which gas is supplied at a higher pressure level. During the pre-blowing phase, compressed air is typically used at a pressure in the interval of 10 bar to 25 bar and during the main blowing phase compressed air is supplied at a pressure in the interval of 25 bar to 40 bar.

From Fig. 3 it can also be seen that in the illustrated embodiment, the heating section (24) from a plurality of revolving transport elements (33) is formed, which are strung together like a chain and guided by guide wheels (34). In particular, it is envisaged to open a substantially rectangular basic contour by the chain-like arrangement. In the illustrated embodiment, in the region of the transfer wheel (29) and an input wheel (35) facing extension of the heating section (24) a single relatively large-sized guide wheel (34) and in the region of adjacent deflections two comparatively smaller dimensioned guide wheels (36) used , In principle, however, any other guides are conceivable.

To enable a dense arrangement of the Transfer wheel (29) and the input wheel (35) relative to each other, the arrangement shown to be particularly useful because in the region of the corresponding extent of the heating section (24) three guide wheels (34, 36) are positioned, in each case the smaller deflection wheels (36 ) in the region of the transition to the linear curves of the heating section (24) and the larger deflection wheel (34) in the immediate transfer area to the transfer wheel (29) and the input wheel (35). As an alternative to the use of chain-like transport elements (33), it is also possible, for example, to use a rotating heating wheel.

After a finished blowing of the containers (2) they are led out of the region of the blow stations (3) by a removal wheel (37) and transported via the transfer wheel (28) and a delivery wheel (38) to the delivery line (32).

In the modified heating section shown in Fig. 4. (24) can be tempered by the larger number of radiant heaters (30) a larger amount of preforms (1) per unit time. The fans (31) introduce cooling air into the region of cooling air ducts (39), which in each case oppose the associated radiant heaters (30) and emit the cooling air via outflow openings. By arranging the outflow directions, a flow direction for the cooling air is realized substantially transversely to a transport direction of the preforms (1). The cooling air ducts (39) can provide reflectors for the heating radiation in the area opposite the radiant heaters (30), and it is likewise possible to realize cooling of the radiant heaters (30) via the discharged cooling air.

Fig. 5 shows an adjusting device (41), which is arranged in the region of a supply line (42) between a resource source (43) for a pneumatic equipment and a receiving device (44) for workpieces. As a resource source (43), for example, a compressor or a vacuum pump can be used. The receiving device (44) can be realized as a blowing station (3) or as a plasma station for the plasma treatment of workpieces.

In the embodiment shown in Fig. 5, the adjusting device (41) is realized as a two-stage controlled proportional valve. A main stage (65) of the actuator (41) and a control regulator (66) are connected in common to the resource source (43), so that no separate line for supplying control air for the control regulator (66) is required. This makes it possible to realize the main stage (65) and the control controller (66) as a unit with internally extending air passages. Via the control regulator (66), a dome pressure control of the main stage (65) and thereby a specification of the resulting pressure in the region of the receiving device (44).

In the embodiment shown in FIG. 6, the adjusting device (41) is also realized as a proportional valve, in which a valve body (46) is positionably arranged in the direction of a valve longitudinal axis (47) within a valve housing (45). To position the valve body (46), a proportional solenoid (48) is used, which displaces the valve body (46) against the force of a return spring (49). In a the valve body (46) receiving the interior (50) of the valve housing (45) open a pressure inlet (51), a pressure outlet (52) and a vent port (53).

In the illustrated embodiment, the valve body (46) is designed substantially cylindrical and in the region of an outer circumferential surface with two circumferential grooves (54, 55) which are separated relative to each other by a separating web (56). The separating web (56) is dimensioned such that it either completely closes the pressure outlet (52) during a longitudinal displacement of the valve body (46) or connects it to a predeterminable flow resistance either with the pressure inlet (51) or the venting connection (53). A current pressure in the region of the pressure outlet (52) is detected via a pressure sensor (57). The pressure sensor (57) is connected to a control device (58) which has a history memory (59) for a nominal value profile of the pressure profile and which is also connected to the electrically actuated proportional magnet (48). Due to the pressure detection with the aid of the pressure sensor (57), the pressure profile predetermined in the region of the history memory (59) can be realized.

Fig. 7 shows typical pressure curves in the blastechnischen production of containers. The pressure profile (60) shows a conventional Blasdruckverlauf when using two blow valves for switching on a Vorblasstufe with a pressure of about 3 bar for a period of about 0.3 seconds and a Hauptblasstufe with a connection of a pressure of about 35 bar for a period of time of about 1 second. For a pressure relief, a vent valve is activated. For the realization of the pressure curve (60) thus typically three valves are used, which are usually designed as two / two-way valves.

The pressure profile (61) was varied with respect to the pressure profile (60) in the region of the pre-blowing region. It is here during pre-blowing a pre-pressure peak of about 8 bar realized with subsequent controlled lowering to about 5 bar. Such a course of the pressure during the pre-blowing phase leads to an improved distribution of material in the blown bottle, since more material is withdrawn from the area of the bottle neck at the beginning of the blowing process.

The pressure profile (62) realized during the Vorblasphase a constantly increasing pressure curve. The pressure rise is here divided into two segments, each with approximately linear course. A transition of the segments into each other takes place in relation to a start of the blowing process after about 0.35 seconds and at about 10 bar instead. The pressure curve in the second linear segment runs at a slightly lower gradient than in the first segment. Such a course of the pressure in the Vorblasphase already leads very early to an approximation of the bottle contour to a planned final contour.

The pressure curve (63) shows after about 1 second, a controlled pressure reduction from about 35 bar to about 23 bar. Such a blow-pressure course utilizes the incipient material consolidation of the blown container and maintains the pressure only to an extent required for sufficient contact of the material of the container with the blow mold to assist in further heat transfer cooling. The pressure reduction mechanically relieves the locking system of the blowing station. Service life of the blow molding can be increased thereby.

Claims (27)

1. Method for pneumatically controlling a blowing machine for the production of containers (2) from injection-moulded preforms (1), wherein, in the region of a supply line (42) between an operating agent source (43) for a pneumatic operating agent and a receiving means (44) for receiving workpieces, a supply of the operating agent is controlled by at least one adjustment means (41) and wherein the adjustment means (41) generates a time-variable pressure in the region of the receiving means (44), characterised in that the adjustment means (41) is regulated in such a way that a predeterminable time characteristic of the pressure is produced during the performance of a blowing process, at least in the environment of a pressure sensor (57) having a predeterminable maximum tolerance, and in that the time flow of a process pressure of a blowing gas for expanding the preform (1) into the container (2) is predetermined.
2. Method according to claim 1, characterised in that an electromechanically actuated valve is controlled as the adjustment means (41).
3. Method according to either claim 1 or claim 2, characterised in that the adjustment means (41) is activated by a programmable controller.
4. Method according to any one of claims 1 to 3, characterised in that a proportional valve is activated as the adjustment means (41).
5. Method according to any one of claims 1 to 4, characterised in that a three-way proportional valve is activated as the adjustment means (41).
6. Method according to any one of claims 1 to 5, characterised in that a pressure supply means is controlled for at least one blowing station (3) positioned on a rotating blowing wheel (25).
7. Method according to any one of claims 1 to 6, characterised in that the adjustment means (41) provides the regulated pressure in close proximity to the receiving means.
8. Method according to any one of claims 1 to 7, characterised in that the adjustment means (41) is conveyed, together with the receiving means, by a rotating support wheel.
9. Method according to any one of claims 1 to 8, characterised in that an excess pressure is controlled.
10. Method according to claim 9, characterised in that a pressure is controlled at a pressure level of up to 40 bar.
11. Method according to any one of claims 1 to 10, characterised in that the pressure is regulated by a two-stage proportional valve.
12. Device for the blow-moulding of containers using a heating means for injection-moulded preforms and a pneumatic controller having an adjustment means (41) which is arranged in the region of a supply line (42) between an operating agent source (43) for a pneumatic operating agent and a receiving means (44) for receiving workpieces and is activated for defining a time-variable pressure in the region of the receiving means (44), characterised in that the adjustment means (41) is coupled to a regulating means (58) having a connection to at least one pressure sensor (57) and in that the regulating means (58) has a pattern memory (59) for a desired value profile of the pressure flow time during the performance of a blowing process and is coupled to a sequence controller (64) which cyclically defines generation of the pressure flow corresponding to the stored desired value profile in such a way that the time flow of a process pressure of a blowing gas for expansion of the preform (1) into the container (2) is defined.
13. Device according to claim 12, characterised in that the adjustment means (41) is configured as an electrically controlled valve.
14. Device according to either claim 12 or claim 13, characterised in that the sequence controller (64) is configured as a programmable controller.
15. Device according to any one of claims 12 to 14, characterised in that the adjustment means (41) is configured as a proportional valve.
16. Device according to any one of claims 12 to 14, characterised in that the adjustment means (41) is configured as a three-way proportional valve.
17. Device according to any one of claims 12 to 16, characterised in that the adjustment means (41) is connected to at least one blowing station (3) arranged on a rotating blowing wheel (25).
18. Device according to any one of claims 12 to 17, characterised in that the adjustment means (41) is arranged in close proximity to the receiving means.
19. Device according to any one of claims 12 to 18, characterised in that the adjustment means (41) is arranged, together with the receiving means, on a rotating support wheel.
20. Device according to any one of claims 12 to 19, characterised in that the adjustment means (41) is configured for regulating an excess pressure.
21. Device according to claim 20, characterised in that the adjustment means (41) is configured for regulating an excess pressure at a pressure of up to 40 bar.
22. Device according to any one of claims 12 to 21, characterised in that the adjustment means (41) is configured for carrying out a two-stage regulation process.
23. Device according to any one of claims 12 to 22, characterised in that the adjustment means (41) is provided with a flow path which can be sealed by a valve body (46) at least in certain regions.
24. Device according to any one of claims 12 to 23, characterised in that an interior (50) of the adjustment means (41) is connectable to the operating agent source (43) via a pressure inlet (51).
25. Device according to any one of claims 12 to 24, characterised in that the interior (50) of the adjustment means (41) is connectable to an environment via a ventilation connection (53).
26. Device according to any one of claims 12 to 25, characterised in that the interior (50) of the adjustment means (41) is connectable to the receiving means (44) via a pressure outlet (52).
27. Device according to any one of claims 12 to 26, characterised in that the valve body (46) of an electrically controlled proportional magnet (48) is arranged so that it can be positioned counter to a force of a readjusting spring (49).

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